Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory.
It acts to replace and recover from the activities of living. Its action is (almost always) the opposite of the sympathetic division. It activates the gut for digestion, slows the heart rate, decreases the blood pressure, etc. The autonomic nervous system controls the insides of the body: the viscera or gut.
Sympathetic Pathways. Neurons of the sympathetic division of the autonomic nervous system are aggregated into two main collections of ganglia: the paravertebral ganglia, which form the sympathetic chain each side of the vertebral column, and the prevertebral ganglia lying around the origins of the coeliac and mesenteric arteries ( Figure 1).